docs: def get_conversion_factor(self, in_nc, num_nc_files):
          """get conversion_factor"""
          data_in_nc = Dataset(in_nc)
  
          # convert from kg/m^2 (i.e. mm) to m
          conversion_factor = 0.001
  
          # ECMWF units are in m
          if data_in_nc.variables[self.runoff_vars[0]] \
                  .getncattr("units") == "m":
              conversion_factor = 1
  
          # ftp://hydro1.sci.gsfc.nasa.gov/data/s4pa/GLDAS_V1/README.GLDAS.pdf
          if "s" in data_in_nc.variables[self.runoff_vars[0]] \
                  .getncattr("units"):
              # that means kg/m^2/s in GLDAS v1 that is 3-hr avg,
              # so multiply by 3 hr (ex. 3*3600). Assumed same
              # for others (ex. 1*3600).
              # If combining files, need to take average of these,
              # so divide by number of files
              conversion_factor *= \
                  self.simulation_time_step_seconds / \
                  num_nc_files
          data_in_nc.close()
  
          return conversion_factor